Knead butter in pieces, 75 g icing sugar, flour, vanilla extract and egg first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Wrap the dough in foil and chill for approx. 30 minutes
Roll out the dough in portions on a floured work surface to a thickness of approx. 4 mm. Cut out a total of approx. 30 hearts (approx. 6 cm Ø) and cut a hole in the middle with a smaller heart cutter (approx. 1.5 cm Ø). Knead the remains again and again, roll out again. Spread the biscuits on 2 baking trays lined with baking paper. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) one after the other for 12-15 minutes. Take out the biscuits and let them cool down
Sift 250 g icing sugar into a bowl and stir with grenadine until smooth and slightly thicker. If necessary, stir in 1-2 tbsp. more water. Spread the hearts with it and let them dry
waiting time approx. 2 hours